Sol-gel coating compositions including corrosion inhibitor-encapsulated layered double hydroxide and related processes

ABSTRACT

A Zn—Al layered double hydroxide (LDH) composition is added to a solution including a corrosion inhibitor and stirred, and a precipitate of the solution is collected, washed, and dried to form a corrosion inhibiting material (CIM), in which the LDH composition is intercalated with the corrosion inhibitor. An inorganic CIM and/or an organic CIM may be formed. The organic CIM may be added to a sol-gel composition to form an organic CIM-containing sol-gel composition, and the inorganic CIM may be added to a sol-gel composition to form an inorganic CIM-containing sol-gel composition. Further, the organic CIM-containing sol-gel composition may be applied on a substrate (e.g., an aluminum alloy substrate) to form an organic CIM-containing sol-gel layer and cured by ultraviolet (UV) radiation, the inorganic CIM-containing sol-gel composition may be applied on the substrate to form an inorganic CIM-containing sol-gel layer and cured by UV radiation, and the sol-gel layers may be thermally cured.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of and priority to U.S. ProvisionalApplication No. 62/364,657, filed on Jul. 20, 2016, which is herebyincorporated by reference in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to coating compositions and processesand, more particularly, to sol-gel coating compositions includingcorrosion inhibitor-encapsulated layered double hydroxide and relatedprocesses.

2. Related Art

High strength alloys such as aluminum alloys are widely used in variousindustries such as the aerospace industry due to their high strength toweight ratio. However these alloys are prone to corrosion due to thepresence of alloying materials.

In order to protect these alloys from the environment, a chromeconversion coating may be provided on a surface of an alloy followed byapplication of primer and a top coat. Although organic paint systemsapplied on the surface provide good barrier properties againstcorrosion, even small defects formed in the organic paint ensurepathways for the ingress of electrolyte to the metallic surface, whichinitiates localized corrosion. Therefore, chromium based conversioncoatings have been used in anti-corrosion pretreatments beforeapplication of organic coatings. However, hexavalent chromium compoundshave harmful effects.

Thus, there is a need for coating compositions and processes that arechromium-free while providing a coating that is corrosion-resistant.

SUMMARY

In accordance with embodiments of the present disclosure, variousmethods and formulations are provided relating to sol-gel coating ofsubstrates such as an aluminum substrate, an aluminum alloy substrate(e.g., AA 2024, AA6061, or AA7075), or other substrate. The sol-gelcoating provided on a substrate advantageously provides corrosionprotection. Further, the sol-gel coating provided on the substrateadvantageously provides enhanced adhesion between the substrate and apaint system (e.g., primer and paint).

In one exemplary aspect, a method for preparing a corrosion inhibitingmaterial (CIM) includes adding a Zn—Al layered double hydroxide (LDH)composition to a solution including a corrosion inhibiting compound andstirring, collecting a precipitate of the solution, and washing anddrying the precipitate of the solution to form the corrosion inhibitingmaterial in which the corrosion inhibiting compound is intercalated inthe Zn—Al LDH composition. The method may further include mixing a zincnitrate solution and an aluminum nitrate solution and stirring undernitrogen purging to form a mixture, adding a sodium nitrate solution tothe mixture while maintaining a pH ranging from about 8 to about 12 andstirring under nitrogen purging, collecting a precipitate of themixture, and washing and drying the precipitate of the mixture to formthe Zn—Al LDH composition. An organic corrosion inhibiting material maybe formed by using an organic corrosion inhibiting compound (e.g., animidazole such as 1-(3-aminopropyl)imidazole; a triazole such as1H-1,2,3-triazole, 4-methyl-4H-1,2,4-triazole-3-thiol,1,2,4-triazole-3-carboxylic acid, 3-amino-1,2,4-triazole-5-thiol,4H-1,2,4-triazol-4-amine, 3-mercapto-4-methyl-4H-1,2,4-triazole, or5-phenyl-1H-1,2,4-triazole-3-thiol; a tetrazole such as1-methyl-1H-tetrazole-5-thiol or 1H-tetrazole-5-acetic acid; a thiazolesuch as 4-methyl-1,3-thiazole-5-carboxylic acid; a thiadiazole such as1,3,4-thiadiazole-2,5-dithiol; a benzimidazole such as1H-benzimidazole-2-carboxylic acid; a benzotriazole such as1H-benzotriazole; a benzothiazole such as 2-mercaptobenzothiazole; aquinoline such as 8-hydroxyquinoline; phytic acid; an organophosphonicacid such as amino tris(methylenephosphonic acid), ethylenediaminetetra(methylenephosphonic acid), 1-hydroxyethylidene-1,1-diphosphonicacid, or diethylenetriamine penta(methylenephosphonic acid); a vegetableoil such as linseed oil or other vegetable oil containing saturatedand/or unsaturated fatty acids such as stearic acid, palmitic acid,oleic acid, linoleic acid, or linolenic acid; and/or other organiccorrosion inhibiting compound). An inorganic corrosion inhibitingmaterial may be formed by using an inorganic corrosion inhibitingcompound (e.g., a vanadate, a molybdate, a tungstate, a phosphate, amanganate, a permanganate, an aluminate, and/or other inorganiccorrosion inhibiting compound).

In an additional exemplary aspect, a method for preparing aCIM-containing sol-gel composition includes adding the corrosioninhibiting material to a sol-gel composition to form the CIM-containingsol-gel composition. The amount of the corrosion inhibiting materialthat is added may range from about 1 to about 10 parts by weight per 100parts by weight of the sol-gel composition. The method may furtherinclude contacting a first alkoxysilane with water and an inorganic acidto form a first composition, contacting a zirconium alkoxide with anorganic acid to form a second composition, contacting the firstcomposition with the second composition to form a mixture, contactingone or more second alkoxysilanes and an organic acid with the mixture toform the sol-gel composition, the sol-gel composition having a ratio ofa number of moles of silicon to a number of moles of zirconium(n_(Si)/n_(Zr)) ranging from about 2 to about 10, and adding aphotoinitiator to the sol-gel composition. An organic CIM-containingsol-gel composition may be formed by using an organic corrosioninhibiting material. An inorganic CIM-containing sol-gel composition maybe formed using an inorganic corrosion inhibiting material.

In another exemplary aspect, a method for providing acorrosion-resistant coating on a substrate includes forming thecorrosion-resistant coating including multiple sol-gel layers on thesubstrate using the organic CIM-containing sol-gel composition and theinorganic CIM-containing sol-gel composition. The multiple sol-gellayers may be formed by applying the organic CIM-containing sol-gelcomposition on the substrate to form one or more organic CIM-containingsol-gel layers, curing the one or more organic CIM-containing sol-gellayers by UV radiation, applying the inorganic CIM-containing sol-gelcomposition on the substrate to form one or more inorganicCIM-containing sol-gel layers, curing the one or more second sol-gellayers by the UV radiation, and thermally curing multiple sol-gel layersincluding the one or more organic CIM-containing sol-gel layers and theone or more inorganic CIM-containing sol-gel layers. The method mayfurther include applying primer and/or paint on the multiple sol-gellayers of the substrate, the multiple sol-gel layers facilitatingadherence of the primer or the paint to the substrate.

In yet another exemplary aspect, a corrosion inhibiting material, aCIM-containing sol-gel composition, and/or a corrosion-resistant coatingthat includes multiple sol-gel layers may be provided by any of theabove methods.

In a further exemplary aspect, a corrosion-resistant coated productincludes a plurality of sol-gel layers on a substrate, the plurality ofsol-gel layers including at least one organic CIM-containing sol-gellayer and at least one inorganic CIM-containing sol-gel layer. Theorganic CIM-containing sol-gel layer includes an organic corrosioninhibiting material and a polymer composite of one or morealkoxysilanes, a zirconium alkoxide, and an organic acid. The organiccorrosion inhibiting material includes a Zn—Al layered double hydroxide(LDH) composition encapsulating an organic corrosion inhibitingcompound. The inorganic CIM-containing sol-gel layer includes aninorganic corrosion inhibiting material and a polymer composite of oneor more alkoxysilanes, zirconium alkoxide, and an organic acid. Theinorganic corrosion inhibiting material includes a Zn—Al LDH compositionencapsulating an inorganic corrosion inhibiting compound.

The scope of the invention is defined by the claims, which areincorporated into this section by reference. A better understanding ofthe methods and formulations for sol-gel coating of the presentdisclosure, as well as an appreciation of the above and additionaladvantages thereof, will be afforded to those of skill in the art by aconsideration of the following detailed description of one or moreexample embodiments thereof. In this description, reference is made tothe various views of the appended sheets of drawings, which are brieflydescribed below, and within which, like reference numerals are used toidentify like ones of the elements illustrated therein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example process for preparing a corrosioninhibiting material in accordance with an embodiment of the presentdisclosure.

FIG. 2 illustrates an example process for preparing a Zn—Al layereddouble hydroxide (LDH) composition in accordance with an embodiment ofthe present disclosure.

FIG. 3 illustrates an example process for preparing a sol-gelcomposition in accordance with an embodiment of the present disclosure.

FIG. 4 illustrates an example process for forming a corrosion-resistantcoating that includes one or more sol-gel layers on a substrate inaccordance with an embodiment of the present disclosure.

FIG. 5 illustrates an example corrosion-resistant coating that includesan inorganic CIM-containing sol-gel layer and an inorganicCIM-containing sol-gel layer formed by the process of FIG. 4 inaccordance with embodiments of the present disclosure.

FIG. 6A is an SEM image of a Zn—Al layered double hydroxide (LDH) powderas prepared by the process of FIG. 2.

FIG. 6B is an energy-dispersive X-ray spectrum of the Zn—Al LDHcomposition of FIG. 6A.

FIG. 7A is an SEM image of a mercaptobenzothiazole-exchanged Zn—Al LDHcomposition as prepared by the process of FIG. 3.

FIG. 7B is an energy-dispersive X-ray spectrum of themercaptobenzothiazole-exchanged Zn—Al LDH composition of FIG. 7A.

FIG. 8A is an SEM image of a vanadate-exchanged Zn—Al LDH composition asprepared by the process of FIG. 3.

FIG. 8B is an energy-dispersive X-ray spectrum of the vanadate-exchangedZn—Al LDH composition of FIG. 8A.

FIGS. 9A and 9B are images of sol-gel coated substrates formed by theprocess of FIG. 4 after a corrosion-resistance test.

FIG. 9B is an image of a sol-gel coated substrate formed by the processof FIG. 4 after a corrosion-resistance test.

FIG. 9C is an image of a chrome conversion coated substrate after acorrosion-resistance test.

FIG. 9D is an image of an uncoated substrate after acorrosion-resistance test.

FIG. 10 is an image of a primer applied sol-gel coated substrate formedby the process of FIG. 4 after an adhesion test.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses.

The terms “substituent”, “radical”, “group”, “moiety,” and “fragment”may be used interchangeably.

Singular forms “a” and “an” may include plural reference unless thecontext clearly dictates otherwise.

The number of carbon atoms in a substituent can be indicated by theprefix “C_(A-B)” where A is the minimum and B is the maximum number ofcarbon atoms in the substituent.

The term “alkyl” embraces a linear or branched acyclic alkyl radicalcontaining from 1 to about 15 carbon atoms. In some embodiments, alkylis a C₁₋₁₀ alkyl, C₁₋₆ alkyl, or C₁₋₃ alkyl radical. Examples of alkylinclude, but are not limited to, methyl, ethyl, propyl, isopropyl,butyl, isobutyl, tert-butyl, sec-butyl, pentan-3-yl

and the like.

The term “alkoxy” is RO— where R is alkyl. Non-limiting examples ofalkoxy include methoxy, ethoxy, propoxy, n-butyloxy, and tert-butyloxy.The terms “alkyloxy”, “alkoxy,” and “alkyl-O—” may be usedinterchangeably.

The term “methacryl”

The term “methacryloxy” is

The term “methacryloxyalkyl” embraces alkyl substituted withmethacryloxy. Non-limiting examples of methacryloxyalkyl includemethacryloxyethyl, methacryloxypropyl, and methacryloxybutyl.

The term “glycidyl” is

The term “glycidyloxy” is

The terms “glycidyloxy” and “glycidoxy” may be used interchangeably.

The term “glycidoxyalkyl” embraces alkyl substituted with glycidoxy.Non-limiting examples of glycidoxyalkyl include, glycidoxyethyl, andglycidoxypropyl, and glycidoxybutyl. The terms “glycidyloxyalkyl” and“glycidoxyalkyl” may be used interchangeably.

The term “aminoalkyl” embraces an amino radical attached to a parentmolecular scaffold through an alkyl radical (e.g., NH₂-alkyl-scaffold).

The term “aryl” refers to any monocyclic, bicyclic, or tricycliccyclized carbon radical, wherein at least one ring is aromatic. Anaromatic radical may be fused to a non-aromatic cycloalkyl orheterocyclyl radical. Aryl may be substituted or unsubstituted. Examplesof aryl include phenyl and naphthyl.

The term “aralkyl” embraces aryl attached to a parent molecular scaffoldthrough alkyl and may be used interchangeably with the term “arylalkyl.”Examples of aralkyl include benzyl, diphenylmethyl, triphenylmethyl,phenylethyl, and diphenylethyl. The terms “benzyl” and “phenylmethyl”may be used interchangeably.

The term “silane” is a compound containing silicon.

The term “organosilane” is a silane having at least one silicon tocarbon bond.

The term “alkoxysilane” is a silane having at least one silicon toalkoxy bond.

The term “organoalkoxysilane” is a silane having at least one silicon tocarbon bond and at least one silicon to alkoxy bond.

The term “about,” as used herein when referring to a measurable valuesuch as an amount, concentration, time and the like, is meant toencompass variations of ±20%, ±10%, ±5%, ±1%, ±0.5%, or even ±0.1% ofthe specified value.

Compositions and processes relating to sol-gel coating of substratessuch as metal or metal alloy substrates (e.g., aluminum substrates,aluminum alloy substrates (e.g., AA 2024, AA6061, or AA7075), or othersubstrates) are provided. Sol-gel coating may be used as a chrome-freepretreatment on substrates prior to the application of organic coatingssuch as primer and paint. The pretreatment may be performed by applyinga layer of a sol-gel composition that includes a corrosion inhibitingmaterial (CIM). The sol-gel composition is obtained as a product ofhydrolysis and condensation of a mixture of organosilanes and a metalalkoxide, along with a corrosion inhibitor (also referred to as acorrosion inhibiting compound) encapsulated in nanocarriers (alsoreferred to as nanocontainers or nanoparticles) made up of layereddouble hydroxide (LDH) such as Zn—Al LDH. Nanocarriers have a sizeranging from about 1 nm to about 1000 nm. Ultraviolet (UV) radiation isused to densify the sol-gel layer in addition to, or instead of, thermalcuring the sol-gel layer. Thermal curing may include exposing thesol-gel layer to a high temperature (e.g., in a hot air circulatedoven). Alternatively, or in addition, thermal curing may includeexposing the sol-gel layer to infrared (IR) radiation or near IRradiation, which reduces curing time. Advantageously, the sol-gelcoating composition may be low temperature curable, provide excellentbarrier protection, and possess self-healing properties to renderprolonged corrosion protection. Further, the sol-gel layers formed usingthe sol-gel coating composition may release corrosion inhibitingcompounds on demand.

FIG. 1 illustrates an example process 100 for preparing a corrosioninhibiting material. The corrosion inhibiting material includes alayered double hydroxide (LDH) composition (e.g., a Zn—Al LDHcomposition) encapsulating one or more corrosion inhibiting compounds.The corrosion inhibiting material may be an organic corrosion inhibitingmaterial that includes one or more organic corrosion inhibitingcompounds, an inorganic corrosion inhibiting material that includes oneor more organic corrosion inhibiting compounds, or a combinationcorrosion inhibiting material that includes one or more organiccorrosion inhibiting compounds and one or more inorganic corrosioninhibiting compounds.

At block 102, a solution of corrosion inhibiting compound is prepared.For example, an organic corrosion inhibiting compound is dissolved ordispersed in a solvent to form the solution. In another example, aninorganic corrosion inhibiting compound is dissolved in a solvent toform the solution. In a further example, an organic corrosion inhibitingcompound and an inorganic corrosion inhibiting compound is dissolved ina solvent to form the solution.

In an aspect, the organic corrosion inhibiting compound is an imidazole,a triazole, a tetrazole, a thiazole, a thiadiazole, a benzimidazole, abenzotriazole, a benzothiazole, a quinoline, phytic acid, anorganophosphonic acid, or an oil. The oil includes saturated and/orunsaturated fatty acids such as stearic acid, palmitic acid, oleic acid,linoleic acid, and/or linolenic acid. The oil may be a vegetable oilsuch as linseed oil or other vegetable oil.

Specific examples of the organic corrosion inhibiting compound include1-(3-aminopropyl)imidazole, 1H-1,2,3-triazole,4-methyl-4H-1,2,4-triazole-3-thiol, 1,2,4-triazole-3-carboxylic acid,3-amino-1,2,4-triazole-5-thiol, 4H-1,2,4-triazol-4-amine,3-mercapto-4-methyl-4H-1,2,4-triazole,5-phenyl-1H-1,2,4-triazole-3-thiol, 1-methyl-1H-tetrazole-5-thiol,1H-tetrazole-5-acetic acid, 4-methyl-1,3-thiazole-5-carboxylic acid,1,3,4-thiadiazole-2,5-dithiol, 1H-benzimidazole-2-carboxylic acid,1H-benzotriazole (BTA), 2-mercaptobenzothiazole (MBT),8-hydroxyquinoline, phytic acid, amino tris(methylenephosphonic acid)(ATMP), ethylenediamine tetra(methylenephosphonic acid) (EDTMP),1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), diethylenetriaminepenta(methylenephosphonic acid) (DTPMP), and linseed oil.

In an aspect, the inorganic corrosion inhibiting compound is a salt ofan oxyanion of a transition metal, a post-transition metal, a metalloid,or a polyatomic non-metal.

In another aspect, the inorganic corrosion inhibiting compound is avanadate, a molybdate, a tungstate, a phosphate, a manganate, apermanganate, or an aluminate.

Specific examples of the inorganic corrosion inhibiting compound includesodium metavanadate, potassium permanganate, sodium molybdate, andsodium tungstate.

At block 104, a Zn—Al LDH composition is prepared. For example, theZn—Al LDH compound may be prepared by a process 200 of FIG. 2.

At block 106, the Zn—Al LDH composition is added to the solution of thecorrosion inhibiting compound. For example, the Zn—Al LDH composition inan amount ranging from about 5 to about 100 g per 1 L of the solution isadded to the solution with stirring and stirring is continued for a timeperiod ranging from 3 to about 48 h. The amount of the Zn—Al LDHcomposition may be 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65,70, 75, 80, 85, 90, 95, or 100 g per 1 L of the solution, where anyvalue may form an upper end point or a lower end point, as appropriate.The time period may be about 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33,36, 39, 42, 45, or 48 h, where any value may form an upper end point ora lower end point, as appropriate. A corrosion inhibitor encapsulatedLDH precipitate is formed as a result of block 106. The Zn—Al LDH isintercalated with the corrosion inhibiting compound such that the Zn—AlLDH composition functions as nanocontainers that encapsulate thecorrosion inhibiting compound.

At block 108, the precipitate of the solution of the corrosioninhibiting compound is collected, for example, by centrifugation. Theprecipitate is washed at block 110 and dried at block 112 to form thecorrosion inhibiting material. For example, the precipitate is washedwith hot water until the pH of the supernatant is neutral, and thendried in a drying oven. The corrosion inhibiting material includes acorrosion inhibiting compound-exchanged Zn—Al LDH composition (alsoreferred to as a corrosion inhibiting compound-incorporated Zn—Al LDHcomposition, a corrosion inhibiting compound-intercalated Zn—Al LDHcomposition or a corrosion inhibiting compound-encapsulated Zn—Al LDHcomposition).

If an organic corrosion inhibiting compound was used in block 102, thecorrosion inhibiting material is an organic corrosion inhibitingmaterial that includes the organic corrosion inhibiting compoundencapsulated in the Zn—Al LDH composition. If an inorganic corrosioninhibiting compound was used in block 102, the corrosion inhibitingmaterial is an organic corrosion inhibiting material that includes theorganic corrosion inhibiting compound encapsulated in the Zn—Al LDHcomposition. Accordingly, in embodiments in which both an inorganiccorrosion inhibiting material and an organic corrosion inhibitingmaterial are desired, process 100 may be performed twice, once using anorganic corrosion inhibiting compound at block 102 and once using aninorganic corrosion inhibiting compound at block 102.

In some embodiments, a combination corrosion inhibiting material thatincludes the Zn—Al LDH composition encapsulating both an organiccorrosion inhibiting compound and an inorganic corrosion inhibitingcompound may be formed by mixing an organic corrosion inhibitingmaterial and an inorganic corrosion inhibiting compound each prepared byrespective process 100, or by preparing a solution including both typesof corrosion inhibiting compounds at block 102 in one process 100.

EXAMPLE 1

For a vanadate-based corrosion inhibiting material, 400 ml of sodiummetavanadate (NaVO₃) solution having a concentration of about 0.1 M wasprepared. The pH of this solution was adjusted to a pH ranging fromabout 8 to about 9 by addition of a NaOH solution having a concentrationof about 2.0 M. To this, 10 g of a Zn—Al LDH composition was added withcontinuous stirring. Stirring was continued for 24 h. The powder wascentrifuged after 24 h, washed with hot water until the pH of thesupernatant was neutral, and followed by drying the vanadate-exchangedZn—Al LDH composition at 60° C. for a time period ranging from about 3to about 4 h in a drying oven. Similarly, different corrosion inhibitingmaterials were prepared by using a number of different molecules such as2-mercaptobenzothiazole, benzotriazole, 1,3,4-thiadiazole-2,5-dithiol,1-methyl-1-tetrazole-5-thiol, 4-methyl-4H-1,2,4-triazole-3-thiol,8-hydroxyquinoline, phytic acid, an organophosphonic acid, and linseedoil as examples. Other corrosion inhibiting materials may be preparedusing other organic corrosion inhibiting compounds (e.g., imidazoles,triazoles, thiazoles, vegetable oils such as linseed oil) or inorganiccorrosion inhibiting compounds in other examples.

FIG. 2 illustrates an example process 200 for preparing a Zn—Al LDHcomposition. For example, block 104 of FIG. 1 may be performed byprocess 200.

At block 202, a solution of a zinc salt (e.g., zinc nitrate or otherzinc salt) and a solution of aluminum salt (e.g., aluminum nitrate orother aluminum salt) is mixed to form a solution of zinc and aluminum.For example, zinc nitrate is dissolved in a solvent, aluminum nitrate isdissolved in a solvent, and the zinc nitrate solution and the aluminumsolution is mixed and stirred under nitrogen purging to form thesolution of zinc and aluminum, also referred to as a mixture.

At block 204, a solution of an alkali metal salt such as a sodium salt(e.g., sodium nitrate or other sodium salt) is added to the mixture. Forexample, a solution of sodium nitrate is added drop-wise to the mixturewhile maintaining a pH ranging from about 8 to about 11 using a basesolution (e.g., a 2.0 M sodium hydroxide solution or other basesolution). The maintained pH may be about 8, 8.5, 9, 9.5, 10, 10.5, or11, where any value may form an upper end point or a lower end point, asappropriate. A fluffy white precipitate is formed in the resultingmixture. Once the addition of the sodium nitrate solution is complete,at block 206, the mixture is stirred vigorously under nitrogen purgingfor a time period ranging from about 3 hours to 24 hours. The timeperiod may be about 3, 6, 9, 12, 15, 18, 21, or 24 h, where any valuemay form an upper end point or a lower end point, as appropriate.

At block 208, the precipitate of the mixture is collected, for example,by centrifugation. The precipitate is washed at block 210 and dried atblock 212 to form the Zn—Al LDH composition. For example, theprecipitate is washed with hot water and then dried in a drying oven.

EXAMPLE 2

A solution of 104.1 g of Zn(NO₃)₂.6H₂O dissolved in 25 ml water and asolution of 65.6 g of Al(NO₃)₃.9H₂O dissolved in 25 ml water was mixedunder vigorous stirring under N₂ purging. To this mixture, 87.5 ml of aNaNO₃ solution having a concentration of about 0.1 M, adjusted to pH 10,was added drop-wise and maintained at a pH of about 10 by adding a NaOHhaving a concentration of about 2.0 M. A fluffy LDH white precipitatewas formed. Once the addition was complete, the entire mixture wasstirred vigorously under N₂ purging for 12 h. The precipitate wascentrifuged at 6500 rpm and washed about 3 or 4 times with hot water (at80° C.), followed by drying at 65° C. for 24 h. A Zn—Al LDH compositionin the form of a powder was formed.

FIG. 3 illustrates an example process 300 for preparing a sol-gelcomposition. A low temperature curable matrix sol is synthesized in twoparts (composition A and composition B), the two parts are mixedtogether, additional compounds are added and stirred, and a corrosioninhibiting material is added to obtain a sol-gel composition.

At block 302, Composition A is prepared from an alkoxysilane such as anorganoalkoxysilane. An alkoxysilane is contacted with water and aninorganic acid (e.g., HCl, HNO₃, H₃PO₄, or other inorganic acid) to formComposition A.

For example, an alkoxysilane is mixed with water and stirred, and aninorganic acid is added to the solution of the alkoxysilane and waterand stirred in an ice bath until the solution turns transparent. Theratio of the number of moles of the alkoxysilane (which is equal to thenumber of moles of silicon from the alkoxysilane) to the number of molesof water (n_(Si)/n_(water)) in Composition A ranges from about 0.5 toabout 2. The ratio may be, for example, about 0.5, 0.6, 0.7, 0.8, 0.9,1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2.0, where anyvalue may form an upper end point or a lower end point, as appropriate.

In an aspect, an alkoxysilane of Formula I is used as Precursor A:R_(A)—Si—(R_(B))₃  Formula Iwherein;

-   R_(A) is methacryloxyalkyl or glycidoxyalkyl; and-   R_(B) is alkoxy.

In another aspect, R_(A) is methacryloxyalkyl (e.g., methacryloxymethyl,methacryloxyethyl, methacryloxypropyl, methacryloxybutyl, or othermethacryloxyalkyl) or glycidoxyalkyl (e.g., glycidoxymethyl,glycidoxyethyl, glycidoxypropyl, glycidoxybutyl); and each R_(B) isindependently alkoxy (e.g., methoxy, ethoxy, propoxy).

Specific examples of R_(A)—Si—(R_(B))₃ include3-methacryloxypropyltrimethoxysilane,3-methacryloxypropyltriethoxysilane,3-glycidyloxypropyltrimethoxysilane, and 3-glycidoxypropylethoxysilane.

In some aspects, an alkoxysilane used as Precursor A of a sol-gelcomposition includes methacryloxyalkyl alkoxysilane (an alkoxysilane ofFormula I in which R_(A) is methacryloxyalkyl) and/or a glycidoxyalkylalkoxysilane (an alkoxysilane of Formula I in which the R_(A) isglycidoxyalkyl). The methacryloxyalkyl alkoxysilane and/or theglycidoxyalkyl alkoxysilane are used, for example, to facilitatepolymerization of the sol-gel composition when exposed to UV radiation.

At block 304, Composition B is prepared from a transition metal alkoxidesuch as a zirconium alkoxide. A zirconium alkoxide is contacted with anorganic acid such as a carboxylic acid (e.g., methacrylic acid (MAA) orother carboxylic acid) to form Composition B.

For example, the zirconium alkoxide is mixed with methacrylic acid andstirred. The ratio of the number of moles of the zirconium alkoxide(which is equal to the number of moles of zirconium from the zirconiumalkoxide) to the ratio of the number of moles of methacrylic acid((n_(Zr)/n_(MAA)) ranges from about 0.5 to about 2. The ratio may be,for example, about 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4,1.5, 1.6, 1.7, 1.8, 1.9, or 2.0, where any value may form an upper endpoint or a lower end point, as appropriate.

In an aspect, a zirconium alkoxide of Formula II is used as Precursor B:Zr—(R_(C))₄  Formula IIwherein;

-   R_(C) is alkoxy.

In another aspect, each R_(C) is independently alkoxy (methoxy, ethoxy,n-propoxy, isopropoxy, n-butoxy, tert-butoxy, or other alkoxy).

Specific examples of Zr—(R_(C))₄ include zirconium ethoxide, zirconiumn-propoxide, zirconium isopropoxide, zirconium n-butoxide, and zirconiumtert-butoxide.

In some aspects, a zirconium alkoxide is used as Precursor B of asol-gel composition, for example, to match the coefficient of thermalexpansion of the sol-gel composition with a substrate. The zirconiumalkoxide may be used in an amount such that the coefficient of thermalexpansion of the sol-gel composition is equal to or about thecoefficient of thermal expansion of the substrate.

At block 306, Composition A and Composition B are mixed together. Forexample, Composition B is added to Composition A under stirring to avoidagglomeration, and the mixture of Composition A and Composition B isstirred in an ice bath and then stirred at room temperature so that thetemperature of the mixture reaches room temperature.

At block 308, one or more alkoxysilanes such as one or moreorganoalkoxysilanes are added to the mixture of Composition A andComposition B. One or more alkoxysilanes and an organic acid such as acarboxylic acid (e.g., methacrylic acid or other carboxylic acid) arecontacted with the mixture of Composition A and Composition B to form asol-gel composition.

For example, each of one or more alkoxysilanes are added to the mixtureand stirred. Then, methacrylic acid is added to the resulting mixtureand stirred. Optionally, an inorganic acid is added before, togetherwith, or after the organic acid.

In an aspect, one or more alkoxysilane of Formula III is used asPrecursor C:R_(D)—Si—(R_(E))₃  Formula IIIwherein;

-   R_(D) is aryl, aralkyl, glycidoxyalkyl, or aminoalkyl; and-   R_(E) is alkoxy.

In another aspect, R_(D) is aryl (e.g., phenyl or other aryl), aralkyl(e.g., benzyl, phenylethyl, phenylpropyl, or other aralkyl),glycidoxyalkyl (e.g., glycidomethyl, glycidoxyethyl, glycidoxypropyl,glycidoxybutyl, or other glycidoxyalkyl), or aminoalkyl (e.g.,aminomethyl, aminoethyl, aminopropyl, aminobutyl, or other aminoalkyl);and each R_(E) is independently alkoxy (e.g., methoxy, ethoxy, propoxy).

Specific examples of R_(D)—Si—(R_(E))₃ include phenyltrimethoxysilane,phenyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane,3-glycidoxypropyltriethoxysilane, 3-aminopropyltrimethoxysilane, and3-aminopropyltriethoxysilane.

In some aspects, one or more alkoxysilanes used as Precursor C of asol-gel composition include an aryl alkoxysilane (an alkoxysilane ofFormula III in which R_(D) is aryl), a glycidyloxyalkyl alkoxysilane (analkoxysilane of Formula III in which R_(D) is glycidoxyalkyl), and/or anaminoalkyl alkoxysilane (an alkoxysilane of Formula III in which R_(D)is aminoalkyl). The aryl alkoxysilane is used, for example, to improvethe barrier properties of a coating formed from the sol-gel composition.The glycidyloxyalkyl alkoxysilane is used, for example, to generate athick coating. The aminoalkyl alkoxysilane is used, for example, toimprove the adhesion of the sol-gel composition to a substrate whendeposited.

In an example, an aryl alkoxysilane is added to the mixture and stirred.Then, an aminoalkyl alkoxysilane is added to the mixture and stirred.Then, a glycidyloxyalkyl alkoxysilane is added to the mixture. Then,methacrylic acid is added and stirred. An inorganic acid may also beadded. The order of the alkoxysilanes that are added may be changed inother examples.

The total amount of the alkoxysilanes, which includes the alkoxysilaneused in block 302 and the one or more alkoxysilanes used in block 308,and the amount of the zirconium alkoxide used in block 304 are such thatthe sol-gel composition has a ratio of a number of moles ofalkoxysilanes (which is equal to the number of moles of silicon from thealkoxysilanes) to a number of moles of zirconium alkoxide (which isequal to the number of moles of zirconium from the zirconium alkoxide)(n_(Si)/n_(Zr)) ranging from about 2 to about 10. The ratio of thenumber of moles of silicon to the number of moles of zirconium(n_(Si)/n_(Zr)) may be about 2, 3, 4, 5, 6, 7, 8, 9, or 10, where anyvalue may form an upper end point or a lower end point, as appropriate.

In some examples, one or more of the stirring performed in blocks 302,304, 306, and/or 308 may be performed for a time period ranging fromabout 10 min to about 120 min. The stirring performed in blocks 302,304, 306, and/or 308, may be performed for a time period of about 10,20, 30, 40, 50, 60, 70, 80, 90, 100, 110, or 120 min, where any valuemay form an upper end point or a lower end point, as appropriate.

At block 310, the sol-gel composition is diluted with a solvent such asalcohol (e.g., isopropanol or other solvent) and stirred. The dilutionof the sol-gel composition, the stirring to age the sol-gel composition,or both (e.g., block 310 entirely) may be omitted in some embodiments.

For example, the sol-gel composition is diluted with isopropanol in aweight ratio of about 1:1. The diluted sol-gel composition, or thesol-gel composition formed by block 308 if dilution is omitted, isstirred to age the sol-gel composition for a time period ranging from 1to about 24 hours (h). The stirring to age the sol-gel composition maybe performed for a time period of about 1, 2, 3, 4, 5, 6, 9, 12, 15, 18,21, or 24 h, where any value may form an upper end point or a lower endpoint, as appropriate.

At block 312, a photoinitiator is added to the sol-gel compositionformed by block 310 (or by block 308 for embodiments in which block 310is omitted) and stirred.

For example, a photoinitiator in an amount ranging from about 0.5 toabout 3 parts by weight per 100 parts by weight of the sol-gelcomposition (the weight of the sol-gel with the photoinitiator to beadded or, alternatively, the weight of the sol-gel before adding thephotoinitiator) is added, and the sol-gel composition with thephotoinitiator is stirred. The amount of the photoinitiator may be about0.5, 1, 1.5, 2, 2.5, or 3 parts by weight per 100 parts of the sol-gelcomposition, where any value may form an upper end point or a lower endpoint, as appropriate. The stirring may be performed for a time periodranging from about 10 to about 60 min. The stirring may be performed fora time period of about 10, 20, 30, 40, 50, or 60 min, where any valuemay form an upper end point or a lower end point, as appropriate. Oncethe photoinitiator is added, exposure of the sol-gel composition tolight may be avoided by covering a container for the sol-gel composition(e.g., using aluminum foil) and/or storing in an amber-coloredcontainer.

At block 314, a corrosion inhibiting material is added to the sol-gelcomposition to form a CIM-containing sol-gel composition.

For example, a corrosion inhibiting material prepared by process 100 ofFIG. 1 in an amount ranging from about 0.5 to about 10 parts by weightper 100 parts by weight of the sol-gel composition (the weight of thesol-gel with the corrosion inhibiting material to be added or,alternatively, the weight of the sol-gel before adding the corrosioninhibiting material) is added to the sol-gel composition and stirred toform a CIM-containing sol-gel composition. The amount of the corrosioninhibiting material may be about 0.5, 1, 1.5, 2, 2.5, 3, 4, 5, 6, 7, 8,9, or 10 parts by weight per 100 parts by weight of the sol-gelcomposition, where any value may form an upper end point or a lower endpoint, as appropriate.

In another example, a corrosion inhibiting material in an amount of thesol-gel composition in an amount ranging from about 1 to about 10 partsby weight per 100 parts by weight of the solid content of the sol-gelcomposition is added to the sol-gel composition and stirred to form aCIM-containing sol-gel composition. The amount of the corrosioninhibiting material may be about 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 partsby weight per 100 parts by weight of the solid content of the sol-gelcomposition, where any value may form an upper end point or a lower endpoint, as appropriate. The sol-gel composition may have a solid contentranging from about 10 to about 70 parts by weight per 100 parts byweight of the sol-gel composition. The sol-gel composition may have asolid content of about 10, 20, 30, 40, 50, 60, or 70 parts by weight per100 parts by weight of the sol-gel composition, where any value may forman upper end point or a lower end point, as appropriate.

If an organic corrosion inhibiting material is added, an organicCIM-containing sol-gel composition is formed. If an inorganic corrosioninhibiting material is added, an inorganic CIM-containing sol-gelcomposition is formed. Accordingly, in embodiments in which both aninorganic CIM-containing sol-gel composition and an organic corrosioninhibiting material are desired, process 300 may be performed twice,once using an organic CIM at block 314 and once using an inorganic CIMat block 314. Alternatively, the sol-gel composition may be divided intotwo or more batches and block 314 may be performed for each desiredCIM-containing sol-gel compositions using a respective CIM.

Blocks 302-314 of process 300 may be performed in the order presented orin a different order and/or one or more blocks may be omitted in someembodiments. For example, blocks 310, 312, and 314 may be performed in adifferent order.

EXAMPLE 3

Composition A was synthesized by mixing 171.5 g of3-methacryloxypropyltrimethoxysilane and 17.0 g of water in a glass jarloaded on a magnetic stirrer. 5.5 grams of 0.1 N HCl was further addedto the mixture. The solution was stirred in an ice bath till thesolution turned transparent. Although3-methacryloxypropyltrimethoxysilane was used in this example, one ormore other alkoxysilanes of Formula I may be used in place of, or inaddition to, 3-methacryloxypropyltrimethoxysilane in other examples.Also, although HCl was used in this example, one or more other inorganicacids may be used in place of, or in addition to, HCl in other examples.

Composition B was synthesized by mixing 11.8 g of methacrylic acid and45.2 g of zirconium n-propoxide under vigorous stirring. Stirring wascontinued for about 2 h. Although zirconium n-propoxide was used in thisexample, one or more other zirconium alkoxides of Formula II may be usedin place of, or in addition to, zirconium n-propoxide in other examples.

Composition B was added to composition A under vigorous stirring toavoid agglomeration by placing the mixture in an ice bath, and themixture was stirred for about 1 h. The jar containing the mixture wasremoved from the ice bath and stirred at room temperature for at least 1hour for the mixture to come to room temperature.

Then 100 g of phenyltrimethoxysilane was added to the mixture ofComposition A and Composition B and stirred for about 1 h, and then 100g of 3-aminopropyltrimethoxysilane was added and stirred for about 1hour. After completion of the 1 h of stirring with3-aminopropyltrimethoxysilane, 25 grams of3-glycidoxypropyltrimethoxysilane was added. Finally, 10 grams ofmethacrylic acid was added followed by 4 g of 0.1 N HCl and stirred fora further duration of 1 h. Although phenyltrimethoxysilane,3-aminopropyltrimethoxysilane, and 3-glycidoxypropyltrimethoxysilanewere used in this example, one or more other methoxysilanes of FormulaIII may be used in place of, or in addition to, phenyltrimethoxysilane,3-aminopropyltrimethoxysilane, and/or 3-glycidoxypropyltrimethoxysilanein other examples.

The resulting mixture was diluted with isopropanol in a weight ratio ofabout 1:1 and stirred for about 3 hours at room temperature for aging.Although the mixture was stirred for about 3 hours, the mixture may beaged for a different time period in other examples, such as stirringovernight. Approximately 1 kg of sol-gel composition ready for coatingapplication was formed. A photoinitiator, IRGACURE® 184, in the amountof about 2% by weight per 100% of the sol-gel composition (including thephotoinitiator) was added and stirred for 30 min. Although IRGACURE® 184was used in this example, one or more other photoinitiators may be usedin place of, or in addition to, IRGACURE® 184 in other examples. Afteradding IRGACURE® 184, the sol-gel composition was kept away from lightto avoid the sol-gel composition from interacting with light.

A corrosion inhibiting material that includes a vanadate-encapsulatedZn—Al LDH composition was added to one batch of the sol-gel compositionto form an inorganic CIM-containing sol-gel composition. Althoughvanadate was used in this example, other inorganic corrosion inhibitingcompounds may be used in other examples. A corrosion inhibiting materialthat includes a mercaptobenzothiazole-encapsulated Zn—Al LDH compositionwas added to another batch of the sol-gel composition to form an organicCIM-containing sol-gel composition. Although 2-mercaptobenzothiazole wasused in this example, other inorganic corrosion inhibiting compounds maybe used in other examples. The solid content of the sol-gel compositionwas about 28 parts by weight per 100 parts by weight of the sol-gelcomposition (including the photoinitiator). To add 5 parts by weight ofthe corrosion inhibiting material per 100 parts by weight of the solidcontent of the sol-gel composition, 1.4 g of the respective corrosioninhibiting compound was added per 100 g of each batch of the sol-gelcomposition and stirred overnight. Although the stirring was carried outovernight in this example, other time periods may be used in otherexamples (e.g., 2 hours may be sufficient for uniform dispersion).

FIG. 4 illustrates an example process 400 for forming acorrosion-resistant coating that includes one or more sol-gel layers(e.g., one or more sol-gel coatings) on a substrate such as a panel(e.g., an aluminum substrate, an aluminum alloy substrate, or othersubstrate). One or more layers of the sol-gel composition are applied toa substrate, each of the one or more layers is cured by UV light, andthen the one or more layers of the sol-gel composition are thermallycured.

At block 402, an organic CIM sol-gel composition prepared by process 300of FIG. 3 is applied to a substrate. For example, the organic CIMsol-gel composition is contacted with the substrate to form an organicCIM-containing sol-gel layer such as by dipping the substrate in theorganic CIM sol-gel composition, by immersing the substrate in theorganic CIM sol-gel composition, by spraying the organic CIM sol-gelcomposition on the substrate, and/or by other methods of applying theorganic CIM sol-gel composition to the substrate. If dip coating isused, the organic CIM-containing sol-gel layers can be deposited using awithdrawals speed ranging from about 1 to about 15 mm/s (e.g., about 5to about 12 mm/s, about 10 mm/s, or other withdrawal speed). Thewithdrawal speed may be about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,14, or 15 mm/s, where any value may form an upper end point or a lowerend point, as appropriate.

At block 404, the organic CIM-containing sol-gel layer formed by block402 is cured by UV radiation. For example, the UV radiation has a lightdose ranging from about 500 to about 1000 mJ/cm². The UV radiation mayhave a light dose of about 500, 550, 600, 650, 700, 750, 800, 850, 900,950, or 1000 mJ/cm², where any value may form an upper end point or alower end point, as appropriate. The curing by UV radiation may beperformed for a time period ranging from about 0.5 to about 30 min. Thetime period may be about 0.5, 1, 2, 3, 4, 5, 10, 15, 20, 25, or 30 min,where any value may form an upper end point or a lower end point, asappropriate.

At block 406, an inorganic CIM sol-gel composition prepared by process300 of FIG. 3 is applied to a substrate. For example, the inorganic CIMsol-gel composition is contacted with the substrate to form an inorganicCIM-containing sol-gel layer such as by dipping the substrate in theinorganic CIM sol-gel composition, by immersing the substrate in theinorganic CIM sol-gel composition, by spraying the inorganic CIM sol-gelcomposition on the substrate, and/or by other methods of applying theinorganic CIM sol-gel composition to the substrate. If dip coating isused, the inorganic CIM-containing sol-gel layers can be deposited usinga withdrawals speed ranging from about 1 to about 15 mm/s (e.g., about 5to about 12 mm/s, about 10 mm/s, or other withdrawal speed). Thewithdrawal speed may be about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,14, or 15 mm/s, where any value may form an upper end point or a lowerend point, as appropriate.

At block 408, the inorganic CIM-containing sol-gel layer formed by block402 is cured by UV radiation. For example, the UV radiation has a lightdose ranging from about 500 to about 1000 mJ/cm². The UV radiation mayhave a light dose of about 500, 550, 600, 650, 700, 750, 800, 850, 900,950, or 1000 mJ/cm², where any value may form an upper end point or alower end point, as appropriate. The curing by UV radiation may beperformed for a time period ranging from about 0.5 to about 30 min. Thetime period may be about 0.5, 1, 2, 3, 4, 5, 10, 15, 20, 25, or 30 min,where any value may form an upper end point or a lower end point, asappropriate.

Blocks 402-404 are performed before blocks 406-408, but the order may bereversed in other embodiments. In some embodiments, blocks 402-404 arerepeated to form one or more additional organic CIM-containing sol-gellayers and/or blocks 406-408 are repeated to form one or more additionalinorganic CIM-containing sol-gel layers. Blocks 402-404 and/or blocks406-408 may be repeated until the desired number of respective sol-gellayers is formed, in an order corresponding to the desired order of therespective CIM-containing sol-gel layers. In some embodiments, blocks404 and/or 408 may be omitted for at least one of the sol-gel layers(e.g., at least one of the sol-gel layers may be air dried or thermallycured instead of curing using UV radiation). For example, curing usingUV radiation may be omitted for the final, top-most sol-gel layer amongthe desired sol-gel layers.

At block 410, the sol-gel layers are thermally cured. For example, themultiple sol-gel layers including an organic CIM-containing sol-gellayer and an inorganic CIM-containing sol-gel layer are thermally curedat a temperature ranging from about 70 to about 90° C. The multiplesol-gel layers may be thermally cured at about 70, 75, 80, 85, or 90°C., where any value may form an upper end point or a lower end point, asappropriate. The thermal curing may be performed for a time periodranging from about 40 to about 120 minutes. The time period may be 40,50, 60, 70, 80, 90, 100, 110, or 120 min, where any value may form anupper end point or a lower end point, as appropriate. In an example, thethermal curing is performed in a hot air circulated oven. Alternatively,or in addition to, thermal curing at a high temperature, the thermalcuring includes exposing the sol-gel layers to infrared (IR) radiation,near IR radiation, and/or microwave radiation. For example, the sol-gellayers are exposed to IR and/or near IR radiation for a time periodranging from about 10 to about 60 min (e.g., 30 min or other timeperiod). The time period of exposure to IR and/or near IR may be about10, 15, 20, 25, 30, 35, 40, 45, 50, 55, or 60 min, where any value mayform an upper end point or a lower end point, as appropriate.

At block 412, primer and/or paint is applied on the sol-gel layers ofthe substrate. For example, the primer is applied on the top-mostsol-gel layer, and the paint is applied on the primer. Advantageously,the cured sol-gel layers not only provide corrosion resistance to thesubstrate but also facilitate adherence of the primer and/or paint tothe substrate.

EXAMPLE 4

Each sol-gel layer of a substrate was UV cured using a conveyorized UVcuring unit. UV curing was performed on both sides of the substrateusing three-medium-pressure-mercury lamp conveyorized UV curing unit.The lamps provided an output of about 120 W/cm with a total wattage/lamp(1 m long)=12 kW. The belt speed was maintained at about 2 m/min duringcuring. The light dose as measured by a UV radiometer was 871 mJ/cm² inthe UV-C region. After UV curing for about 5 minutes, the sol-gel layercoated substrate was subjected to thermal curing in an air circulatedoven at 80° C. for an hour.

FIG. 5 illustrates an example corrosion-resistant coating that includesan inorganic CIM-containing sol-gel layer and an inorganicCIM-containing sol-gel layer formed by process 400 of FIG. 4. An organicCIM-containing sol-gel composition is contacted with substrate 502 toprovide organic CIM-containing sol-gel layer 504, and sol-gel layer 504is UV cured. Then, an inorganic CIM-containing sol-gel composition iscontacted with sol-gel layer 504 to provide an inorganic CIM-containingsol-gel layer 506 on sol-gel layer 504, and sol-gel layer 506 is UVcured. Sol-gel layer 506 is not UV cured in other examples. Then,sol-gel layers 504 and 506 are thermally cured. The order of sol-gellayers 504 and 506 may be reversed in other examples. Further, althoughsol-gel layers including one organic CIM-containing sol-gel layer andone inorganic CIM-containing sol-gel layer is shown in FIG. 5, thecorrosion-resistant coating may include more than one of each type ofsol-gel layer in other examples.

FIG. 6A is a scanning electron microscopy (SEM) image of a Zn—Al LDHcomposition as prepared by process 200 of FIG. 2, and FIG. 6B is anenergy-dispersive X-ray spectra of the Zn—Al LDH composition. FIG. 7A isan SEM image of a mercaptobenzothiazole-exchanged LDH composition asprepared by process 300 of FIG. 3 (e.g., as described in Example 3), andFIG. 7B is an energy-dispersive X-ray spectra of themercaptobenzothiazole-exchanged Zn—Al LDH composition. FIG. 8A is an SEMimage of a vanadate-exchanged LDH composition as prepared by process 300of FIG. 3 (e.g., as described in Example 3), and FIG. 8B is anenergy-dispersive X-ray spectra of the vanadate-exchanged Zn—Al LDHcomposition.

FIG. 9A is an image of a sol-gel coated substrate 900, formed by theprocess of FIG. 4, after a corrosion-resistance test. Sol-gel coatedsubstrate 900 has an organic CIM-containing sol-gel layer that includesa mercaptobenzothiazole-exchanged LDH composition as its organiccorrosion inhibiting material formed on a substrate, and an inorganicCIM-containing sol-gel layer that includes a vanadate-exchanged LDHcomposition as its inorganic corrosion inhibiting material formed on theorganic CIM-containing sol-gel layer. Sol-gel coated substrate 900 wasexposed to a 5% salt spray. FIG. 9A shows sol-gel coated substrate 900after 336 h of the salt spray test.

FIG. 9B is an image of a sol-gel coated substrate 910, formed by theprocess of FIG. 4, after a corrosion-resistance test. Sol-gel coatedsubstrate 910 has an organic CIM-containing sol-gel layer that includesa phytic acid-exchanged LDH composition as its organic corrosioninhibiting material formed on a substrate, and an inorganicCIM-containing sol-gel layer that includes a vanadate-exchanged LDHcomposition as its inorganic corrosion inhibiting material formed on theorganic CIM-containing sol-gel layer. Sol-gel coated substrate 910 wasexposed to a 5% salt spray. FIG. 9B shows sol-gel coated substrate 910after 336 h of the salt spray test.

FIG. 9C is an image of a chromated substrate 920, formed by chromeconversion coating, after a corrosion-resistance test. Chrome conversioncoated substrate 920 was exposed to a 5% salt spray. FIG. 9C showschrome conversion coated substrate 920 after 336 h of the salt spraytest.

FIG. 9D is an image of an uncoated aluminum alloy substrate 930 after acorrosion-resistance test. Uncoated substrate 930 was exposed to a 5%salt spray. FIG. 9D shows uncoated substrate 930 after 336 h of the saltspray test, which was severely corroded.

Sol-gel coated substrate 900 shown in FIG. 9A and sol-gel coatedsubstrate 910 shown in FIG. 9B had no corrosion. Chrome conversioncoated substrate 920 shown in FIG. 9C, although not corroded, haddiscolored. Chrome conversion coating followed by applying a primer andpaint is currently considered the state of the art forcorrosion-resistant coatings for metal or metal alloy substrates.Accordingly, sol-gel coated substrates 900 and 910 shown in FIGS. 9A and9B, respectively, advantageously have a corrosion resistance that iscomparable or better than that of chrome conversion coated substrate920.

FIG. 10 is an image of a primer applied sol-gel coated substrate 1000formed by process 400 of FIG. 4 after an adhesion test. A scribed wettape adhesion test on primer applied sol-gel coated substrate 1000 wasperformed as follows. Primer applied sol-gel coated substrate 1000 wasimmersed in tap water for 24 hours. After 24 hours, primer appliedsol-gel coated substrate 1000 was removed and blot dry with cheesecloth.Using a metal cutting tool (e.g., a razor blade, a scalpel, a knife, orother cutting tool), two parallel 2 inch long scratches were made, ¾ to1 inch apart, through the coating and to the substrate. The parallelscratches were joined with two intersecting lines, or an “X” pattern. Anadhesive tape was applied over the scratched pattern, and the tape waspressed against the test surface with firm hand pressure.(Alternatively, adhesive tape may be applied using a roller). One end ofthe tape was lifted such that a length of about 2 inches on that end ofthe tape was not in contact with the test surface. The minimum remaininglength of the tape in contact with the test surface was approximately 4inches. The lifted-up 2 inch segment of the tape was positioned tocreate an approximate 45 degree angle with the test surface. Theremainder of the tape was removed by pulling up and back with an abruptmotion. For this adhesion test, if the primer comes off the substrate,it implies poor adhesion. If the primer does not come off the substrate,it implies good adhesion. As shown by the result in FIG. 10, the primerof sol-gel coated substrate 1000 did not come off. Thus, the sol-gellayers formed by process 400 of FIG. 4 advantageously have good adhesionto organic paint such as primer and/or paint.

When introducing elements of the present invention or exemplary aspectsor embodiment(s) thereof, the articles “a,” “an,” “the,” and “said” areintended to mean that there are one or more of the elements. The terms“comprising,” “including,” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements. Although this invention has been described with respect tospecific embodiments, the details of these embodiments are not to beconstrued as limitations. Different aspects, embodiments and featuresare defined in detail herein. Each aspect, embodiment or feature sodefined may be combined with any other aspect(s), embodiment(s) orfeature(s) (preferred, advantageous or otherwise) unless clearlyindicated to the contrary. Accordingly, the scope of the invention isdefined only by the following claims.

What is claimed is:
 1. A method comprising: adding a Zn—Al layereddouble hydroxide (LDH) composition to a first solution comprising afirst corrosion inhibiting compound and stirring; collecting aprecipitate of the first solution; and washing and drying theprecipitate of the first solution to form a first corrosion inhibitingmaterial (CIM), the first CIM comprising the first corrosion inhibitingcompound intercalated in the Zn—Al LDH composition.
 2. The method ofclaim 1, further comprising: mixing a zinc nitrate solution and analuminum nitrate solution and stirring under nitrogen purging to form amixture; adding a sodium nitrate solution to the mixture whilemaintaining a pH ranging from about 8 to about 12 and stirring undernitrogen purging; collecting a precipitate of the mixture; and washingand drying the precipitate of the mixture to form the Zn—Al LDHcomposition.
 3. The method of claim 1, further comprising: adding thefirst CIM to a sol-gel composition to form a CIM-containing sol-gelcomposition.
 4. The method of claim 3, further comprising: contacting afirst alkoxysilane with water and an inorganic acid to form a firstcomposition; contacting a zirconium alkoxide with a first organic acidto form a second composition; contacting the first composition with thesecond composition to form a mixture; contacting one or more secondalkoxysilanes and a second organic acid with the mixture to form thesol-gel composition, the sol-gel composition having a ratio of a numberof moles of silicon to a number of moles of zirconium (n_(Si)/n_(Zr))ranging from about 2 to about 10; adding a photoinitiator to the sol-gelcomposition; and diluting the sol-gel composition with a solvent.
 5. Themethod of claim 4, wherein the contacting to form the first compositioncomprises mixing the first alkoxysilane having the formulaR_(A)—Si—(R_(B))₃ with the water and the inorganic acid, wherein theR_(A) is methacryloxyalkyl or glycidyloxyalkyl, and wherein the R_(B) isa methoxy or ethoxy.
 6. The method of claim 4, wherein the contacting toform the second composition comprises mixing a zirconium alkoxide havingthe formula Zr—(R_(C))₄ with methacrylic acid (MAA), and wherein theR_(C) is ethoxy, n-propoxy, isopropoxy, n-butyloxy, or tert-butyloxy. 7.The method of claim 4, wherein the contacting to form the sol-gelcomposition comprises: adding one or more second alkoxysilanes eachhaving the formula R_(D)—Si—(R_(E))₃ to the mixture, wherein the R_(D)is aryl, aminoalkyl, or glycidoxyalkyl, and wherein the R_(E) is methoxyor ethoxy; and adding MAA and stirring.
 8. The method of claim 3,wherein the adding the CIM comprises adding the CIM in an amount rangingfrom about 1 to about 10 parts by weight per 100 parts by weight of thesol-gel composition or ranging from about 1 to about 10 parts by weightper 100 parts by weight of a solid content of the sol-gel composition.9. The CIM-containing sol-gel composition formed by the method of claim3.
 10. The method of claim 1, further comprising: adding the first CIMto a first sol-gel composition to form an organic CIM-containing sol-gelcomposition, wherein the first corrosion inhibiting compound is anorganic corrosion inhibiting compound, and wherein the first CIM is anorganic CIM; adding the Zn—Al LDH composition to a second solutioncomprising an inorganic corrosion inhibiting compound and stirring;collecting a precipitate of the second solution; washing and drying theprecipitate of the second solution to form an inorganic CIM, theinorganic CIM comprising the inorganic corrosion inhibiting compoundintercalated in the Zn—Al LDH composition; and adding the inorganic CIMto a second sol-gel composition to form an inorganic CIM-containingsol-gel composition.
 11. The method of claim 10, further comprising:dispersing the organic corrosion inhibiting compound comprising1-(3-aminopropyl)imidazole, 1H-1,2,3-triazole,4-methyl-4H-1,2,4-triazole-3-thiol, 1,2,4-triazole-3-carboxylic acid,3-amino-1,2,4-triazole-5-thiol, 4H-1,2,4-triazol-4-amine,3-mercapto-4-methyl-4H-1,2,4-triazole,5-phenyl-1H-1,2,4-triazole-3-thiol, 1-methyl-1H-tetrazole-5-thiol,1H-tetrazole-5-acetic acid, 4-methyl-1,3-thiazole-5-carboxylic acid,1,3,4-thiadiazole-2,5-dithiol, 1H-benzimidazole-2-carboxylic acid,1H-benzotriazole (BTA), 2-mercaptobenzothiazole (MBT),8-hydroxyquinoline, phytic acid, an organophosphonic acid, a vegetableoil, or a combination thereof in a solvent to form the first solution.12. The method of claim 10, further comprising: dissolving the inorganiccorrosion inhibiting compound comprising a vanadate, a molybdate, atungstate, a phosphate, a manganate, a permanganate, an aluminate, or acombination thereof in a solvent to form the second solution.
 13. Themethod of claim 10, further comprising: applying the organicCIM-containing sol-gel composition on a substrate to form an organicCIM-containing sol-gel layer, wherein the substrate is selected from thegroup comprising 2024 aluminum alloy, 6061 aluminum alloy, and 7075aluminum alloy; curing the organic CIM-containing sol-gel layer by UVradiation; applying the inorganic CIM-containing sol-gel composition onthe substrate to form an inorganic CIM-containing sol-gel layer; curingthe inorganic CIM-containing sol-gel layer by the UV radiation; andthermally curing a plurality of sol-gel layers comprising the organicCIM-containing sol-gel layer and the inorganic CIM-containing sol-gellayer to form a corrosion-resistant coating.
 14. The method of claim 13,wherein: the curing the organic CIM-containing sol-gel layer and theinorganic CIM-containing sol-gel layer by the UV radiation comprisesexposing a respective one of the sol-gel layers to the UV radiationhaving a light dose ranging from about 500 to about 1000 mJ/cm² for atime period ranging from about 0.5 to 30 min; and the thermally curingthe plurality of sol-gel layers comprise exposing the plurality ofsol-gel layers to infrared (IR) radiation, near IR radiation, microwaveradiation, hot air having a temperature ranging from about 70 to about90° C., or a combination thereof.
 15. The method of claim 13, furthercomprising applying primer and/or paint on the plurality of sol-gellayers on the substrate, the plurality of sol-gel layers facilitatingadherence of the primer or the paint to the substrate.
 16. Thecorrosion-resistant coating formed by the method of claim
 13. 17. Acorrosion-inhibiting material, comprising: a Zn—Al layered doublehydroxide (LDH) composition comprising nanocarriers of Zn—Al LDH; and acorrosion inhibiting compound intercalated in the nanocarriers of Zn—AlLDH.
 18. The corrosion-inhibiting material of claim 17, wherein: thecorrosion inhibiting compound comprises an organic corrosion inhibitingcompound, an inorganic corrosion inhibiting compound, or both; theorganic corrosion inhibiting compound comprises1-(3-aminopropyl)imidazole, 1H-1,2,3-triazole,4-methyl-4H-1,2,4-triazole-3-thiol, 1,2,4-triazole-3-carboxylic acid,3-amino-1,2,4-triazole-5-thiol, 4H-1,2,4-triazol-4-amine,3-mercapto-4-methyl-4H-1,2,4-triazole,5-phenyl-1H-1,2,4-triazole-3-thiol, 1-methyl-1H-tetrazole-5-thiol,1H-tetrazole-5-acetic acid, 4-methyl-1,3-thiazole-5-carboxylic acid,1,3,4-thiadiazole-2,5-dithiol, 1H-benzimidazole-2-carboxylic acid,1H-benzotriazole (BTA), 2-mercaptobenzothiazole (MBT),8-hydroxyquinoline, phytic acid, an organophosphonic acid, a vegetableoil, or a combination thereof; and the inorganic corrosion inhibitingcompound comprises a vanadate, a molybdate, a tungstate, a phosphate, amanganate, a permanganate, an aluminate, or a combination thereof.
 19. Acorrosion-resistant coated product comprising: at least one organiccorrosion inhibiting material (CIM)-containing sol-gel layer comprisingan organic CIM and a polymer composite of one or more alkoxysilanes, azirconium alkoxide, and an organic acid, the organic CIM comprising aZn—Al layered double hydroxide (LDH) composition encapsulating anorganic corrosion inhibiting compound; and at least one inorganicCIM-containing sol-gel layer comprising an inorganic CIM and the polymercomposite of the one or more alkoxysilanes, the zirconium alkoxide, andthe organic acid, the inorganic CIM comprising the Zn—Al LDH compositionencapsulating an inorganic corrosion inhibiting compound.
 20. Thecorrosion-resistant coated product of claim 19, wherein: the one or morealkoxysilanes comprise a methacryloxyalkyl alkoxysilane, an arylalkoxysilane, an aminoalkyl alkoxysilane, and a glycidoxyalkylalkoxysilane; the organic corrosion inhibiting compound comprises1-(3-aminopropyl)imidazole, 1H-1,2,3-triazole,4-methyl-4H-1,2,4-triazole-3-thiol, 1,2,4-triazole-3-carboxylic acid,3-amino-1,2,4-triazole-5-thiol, 4H-1,2,4-triazol-4-amine,3-mercapto-4-methyl-4H-1,2,4-triazole,5-phenyl-1H-1,2,4-triazole-3-thiol, 1-methyl-1H-tetrazole-5-thiol,1H-tetrazole-5-acetic acid, 4-methyl-1,3-thiazole-5-carboxylic acid,1,3,4-thiadiazole-2,5-dithiol, 1H-benzimidazole-2-carboxylic acid,1H-benzotriazole (BTA), 2-mercaptobenzothiazole (MBT),8-hydroxyquinoline, phytic acid, an organophosphonic acid, a vegetableoil, or a combination thereof; and the inorganic corrosion inhibitingcompound comprises a vanadate, a molybdate, a tungstate, a phosphate, amanganate, a permanganate, an aluminate, or a combination thereof.